1. Field of the Invention
The present invention relates to a fuel cell for generating an electric power by the reaction of fuel with an oxidizer. Further, the present invention relates to a small electric equipment using the fuel cell.
2. Related Background Art
A fuel cell uses an electrolyte/electrode joined member, which is composed of an electrolyte membrane sandwiched between a fuel electrode having a catalyst and an oxidizer electrode having a catalyst, as a power generation cell unit. In the electrolyte/electrode joined member, a fuel gas such as a hydrogen gas is caused to flow on the fuel electrode side while an oxidizing gas containing an oxygen gas is caused to flow on the oxidizer electrode side, and these gases electrochemically react with each other through the electrolyte membrane to provide an electromotive force to the outside. Since a single electrolyte/electrode joined member has a small electromotive force of about 0.7 to 0.8 V, a plurality of electrolyte/electrode joined members are connected in series to be used in many cases.
For example, FIG. 3 shows a sectional view of a conventional fuel cell. Electrolyte/electrode joined members, each of which is composed of an electrolyte membrane 31 having a fuel electrode 32 and an oxidizer electrode 33 on the opposite surfaces thereof, are stacked such that the fuel electrodes 32 face the oxidizer electrodes 33, and conductive separators 34 are inserted between the electrolyte/electrode joined members so as to connect the electrolyte/electrode joined members in series. Further, in each separator 34, an oxidizing gas flow path, which supplies an oxidizing gas to an adjacent oxidizer electrode, and a fuel gas flow path, which supplies a fuel gas to an adjacent fuel electrode are formed, respectively. In this case, the oxidizing gas is supplied by taking in air from the atmosphere through a perforated housing 37, and the fuel is supplied from a fuel storage unit. As described above, the conventional separator has the function of separating the fuel from the oxidizer and the function of a spacer for securing a space for supplying the fuel gas and the oxidizing gas.
For example, Japanese Patent Publication No. H04-25673 (page 205, FIG. 3) discloses a configuration such that a plurality of cells are connected in series through a separator composed of a conductive plate having conductive projections. The conductive projections establish parallel flow paths for fuel and an oxidizing gas over the surface of electrodes.
Further, there is proposed a trial for reducing the size of a fuel cell in which electrolyte/electrode joined members are stacked such that the fuel electrodes face each other or the oxidizer electrodes face each other (see Japanese Patent Application Laid-Open No. 2000-058100 (FIG. 1)).
However, the fuel cell having the stack structure disclosed in Japanese Patent Publication No. H04-25673 described above has a problem that the size of the fuel cell depends on the thickness of the separator and is large in a stack direction. Further, it is important for the separator to secure the flow paths of an oxidizer and fuel and to maximize a reacting electrode interface in order to improve the efficiency of the fuel cell. For this purpose, a contact interface between the separator and the electrodes needs to be reduced.
Further, Japanese Patent Application Laid-Open No. 2000-058100 proposes a trial for reducing the size of a fuel cell. For example, there is also proposed a fuel cell the size of which in a stack direction is reduced by stacking electrolyte/electrode joined members such that the fuel electrodes face each other or the oxidizer electrodes face each other and by inserting an insulating separator into each flow path, in which either one of an oxidizing gas flow path and a fuel gas flow path is formed, between the electrolyte/electrode joined members. The separator merely has a role of electrically isolating upper and lower electrodes and keeping a flow path space and therefore does not improve the power generation efficiency of the fuel cell.
Further, in the fuel cell, it is very difficult to accurately form a fine structure for oxidizer and fuel passages.
In view of the above circumstances, it is desirable to provide a fuel cell having a highly efficient electrode-stack structure that can be reduced in size and from which a large amount of electromotive force can be obtained.
Further, it is desirable to provide a small mobile electric equipment such as a digital camera, a digital video camera, a small projector, a small printer, a notebook personal computer, and the like using the fuel cell.